The present invention relates to an apparatus for the acquisition and restoration in real time of a picture or image formed by successive frames of scanning lines. This invention applies to the processing of pictures and particularly the processing of pictures supplied by a video camera with a view to their possible display on a television screen. It relates more specifically to the processing of framed pictures supplied by an electron microscope.
It is known that for the processing of framed images, scanned by successive lines, it is necessary to convert into digital values, the analog signals obtained at the output of a picture production system (the analog-digital converter is called in this case the acquisition system). These digital values are recorded in a memory and, in general, the acquisition and real time display means for a picture formed from successive frames of scanning lines, with which it is possible to process the picture, are constituted in the following manner.
Following the picture production system, these means comprise an analog-digital converter making it possible to convert the analog signals obtained at the output of the picture production means into digital values. These digital values are transferred by means of a communication bus into a recording memory. A processing system is connected to this memory for processing the digital values. A wire address generator makes it possible to ensure the writing and reading of the digital values written in the memory, before or after they have been processed. The processed digital values extracted from the memory are then transmitted to restoration or display means via a digital-analog converter. All the control circuits permitting, optionally in association with processing means, the passage of the digital values supplied by an analog-digital converter connected to the picture production means, are wired circuits which lack any flexibility of use.
It is known, e.g. in television, that each picture or image is framed. This picture is obtained by juxtaposing a certain number of horizontal lines, a group of which constitutes a frame. This frame is renewed several dozen times per second.
The electrical signal corresponding to this picture comprises an analog part, expressing the light intensity, and a part having a pulse-like nature: the synchronizing or sync making it possible to mark or define the line and frame starts (horizontal and vertical synchronization). It is this electrical signal, called the "composite video signal", which is transmitted by all appropriate means and from which it is possible to reconstitute the picture on arrival. It is known per se to convert this analog signal into a succession of digital values for transmission or processing purposes.
The prior art will be better understood by means of the following diagrammatic drawings, wherein show:
FIG. 1 diagrammatically a per se known apparatus for the acquisition and display of a television picture, not using a signal processing system.
FIG. 2 diagrammatically, a known acquisition and display apparatus for a television picture, which uses an acquired signal processing system.
FIG. 3 diagrammatically but in more detailed manner the known apparatus of FIG. 2.
The simplest known acquisition and display apparatus shown in FIG. 1 comprises a video camera 1 (or any other equivalent picture source), an analog-digital converter 2, transmission means 3, a digital-analog converter 4 and restoration or display means, such as a video monitor 5.
The constraints imposed on the conversion and processing means differ to a considerable extent, depending on whether it is transmission or processing which is involved. In the first case, it is merely necessary for these means to have an adequate operating frequency to ensure the faithful restoration of the overall signal, i.e. that part of the signal representing the luminance (quality of the image, fineness, constrast, etc) and that part containing the sync pulses or signals (stability, centering, etc), without it being necessary to take account of the significance of these sync signals. In particular, converters 2 and 4 can operate independently (both of one another and of the transmission means 3) for as long as the minimum frequency condition referred to hereinbefore is satisfied.
The situation is quite different when, following the means for producing the picture and for the analog-digital conversion of the analog signals representing said picture, the digital values undergo processing, prior to their transfer to the digital-analog converter and to the restoration or display means.
FIG. 2 diagrammatically shows a known acquisition and restoration apparatus including a system for the processing of the digital values from an analog-digital converter. In this case, it is necessary that the digital value corresponding to each dot in the image is located at a perfectly defined location within a computer memory. In other words, there must be a biunivocal application between the bidimensional space of the picture and the unidimensional addressing space. This is only possible through referring to the marks of the X, Y coordinates of the picture, or in other words to the horizontal and vertical sync signals, this applying both at the time of acquisition (analog-digital conversion) and at the time of display (digital-analog conversion). Thus, the operation of the converters must be made dependent on the synchronization sources on the one hand, and on the processing memory addressing system on the other, which is shown in FIG. 2. Compared with FIG. 1, FIG. 2 additionally has the control means 6 of the analog-digital converter and the control means 7 of the digital-analog converter, with the corresponding logic links.
Bearing in mind the inevitable redundancy between the control means 6 and 7, it is preferable to refer to FIG. 3, which is operationally equivalent to FIG. 2.
In FIG. 3, as in FIGS. 1 and 2, the general movement of the information or digital values takes place from left to right from production to display (image restoration). The processing means are now subdivided into four functional blocks, i.e. from top to bottom: the actual processing means A, the storage means constituted by a picture store B, control means C and a video sync generator D. The information passes between the analog-digital converter 2 and digital-analog converter 4, the memory and the processing means by data bus K.
Mention is only made in passing of processing means A because, although their presence conditions the complexity of the diagram, their function can be desynchronized from the acquisition and display functions, so that it is possible to process the latter independently. It should be noted that the processing means can be distributed in memory B, if the structure of the latter is suitable. Memory B is a random access informatics memory, so that its structure can differ widely. In can be in particular broken down into modules, with the possibility of simultaneous access to several of these modules (multiaccess). The control means C ensure the biunivocal correspondence between the picture (acquired or restored) and the memory space, by coordinating the conversion operation with the corresponding memory accesses (both output and input). The control means fulfil this function by simultaneously supplying the desired address values on the address bus E intended for memory D and sync signals H and J to the converters.
Finally, the video sync generator D has been separated from the control means in order to take account of the prior art. Thus, such members now exist in the form of single integrated circuits supplying all the signals necessary for obtaining a video image (horizontal and vertical sync pulses, start of image, beam extinction signals, camera control, etc). It should be noted that during acquisition, video synchronization can take place directly on the camera (or extracted from the composite video signal), and suggested at F in FIG. 3. The other term of the alternative is to synchronize the camera 1 with respect to generator D by line G.
Moreover, for each of the television standards the frequency requirements of the video sync generator are very precisely defined and a greater flexibility is obtained as a result of this separation of functions.